Copper adhesive composition

ABSTRACT

Specific thermoplastic compositions which are formulated to be exceptionally useful for adhesion to copper-containing metals are prepared from either glycidyl acrylate grafts of polypropylene based formulations with a minor elastomeric component or low density polyethylene based formulations grafted with acrylic acid and/or glycidyl acrylate and containing a minor elastomeric component.

This is a continuation, application Ser. No. 746,930, filed Dec. 8,1976, wich is a continuation of application Ser. No. 544,276, filed Feb.28, 1975, which is a continuation of application Ser. No. 340,061, filedMar. 12, 1973, all abandoned.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is not related to any other application owned by thesame asignee but it is an improvement over commonly assigned U.S. Pat.No. 3,862,265, entitled "POLYMERS WITH IMPROVED PROPERTIES AND PROCESSTHEREFOR" filed Apr. 3, 1972, which is incorporated herein in itsentirety, by reference, and it is relevant to a copending, commonlyassigned application with the same filing date as Ser. No. 340,061,entitled "FASTENER ARTICLE" Ser. No. 340,446 filed Mar. 12, 1973, nowSer. No. 659,317, filed Feb. 19, 1976 by the same inventor.

PRIOR ART

Copper is a notoriously difficcult substrate to adhere materials tosince it has a highly oxidized surface and bonds can readily rupturethrough the failure of an oxide layer when oxygen diffuses through theadhesive. Certain epoxy adhesives conventionally known are used forbonding materials to copper but they usually give rise to weakintermediate layers which ultimately result in bond failure. Whateversuccess is obtained by the art in adhering materials to a coppersubstrate, usually results from the use of bright, clean copper whichhas been mechanically abraded or which has been vapor degreased and acidetched.

Conventionally a feric chloride/nitric acid acqueous solution is used toobtain the bright copper. The copper surfaces can also be primed with asilane such as an amino silane to improve copper bonding.

A recent U.S. Pat. No. 3,342,647, teaches that bonding of copper sheetscan be obtained by using urea, formamide, or hexamethylene tetraminewhich is decomposed thermally and conventional adhesive then applied tosuch an activated surface.

Conventional type adhesives which are used to bond copper includeepoxides hardened with polyamine, or an ionomer resin a class ofpolymers in which ionized carboxyl groups create ionic crosslinks, suchas Surlyn obtained from DuPont. If hot-melts are to be used, thennylon-type polyamides or polyhydroxy ether polymers can be used.

SUMMARY OF THE INVENTION

Specifically formulated acrylic acid or a glycidyl acrylate graftscontaining a flexible, e.g. elastomeric component, can be used as copperadhesive without elaborate copper surface preparation.

DESCRIPTION OF THE INVENTION WITH PREFERRED EMBODIMENTS

In the Steinkamp and Grail Ser. No. 240,494 application, and thecopending application entitled "FASTENER ARTICLE", a detaileddescription is given to a new class of grafted polymers which areprepared preferably by a novel technique and which demonstrate unusualadhesion capabilities for numerous substrates. Surprisingly it has beenfound that most of the compositions prepared according to the Ser. No.240,494 application exhibited excellent adhesion properties over a widerange of substrates but do not have minimum adhesion capabilitiestowards copper.

It has been discovered and forms the basis of this invention thatcertain highly specific compounds specially formulated and fallingwithin the generic class described in the above mentioned applications,will exhibit outstanding adhesion to copper. Indeed in a directcomparison with the DuPont Surlyn the specific products of the inventionare at least equivalent in one instance and highly superior in otherinstances.

The speicific novel formulations set forth herein will vary in theiradhesive values towards copper over a range slightly beter than Surlynto a range more than twice the adhesive value of Surlyn.

Generally speaking the special copper adhesion thermo-plasticcompositions of the invention can be classified as either polyethylenebased or polypropylene based.

When they are polyethylene based, the significant factor in theirformulation and composition is that direct grafting with either aglycidyl acrylate component or an acrylic acid component to apolyethylene base, without additional modification of the baseformulation, results in compositions which do not adhere well to copper.

In order to obtain maximum copper adhesion values with a polyethylenebased system, there must also be included in the formulation a minoramount of an elastomeric component. Such an elastomeric component can beany elastomer which is compatible with polyethylene, generally lowunsaturated varieties being preferable. Suitable examples includeethylene p lene copolymers, butyl rubbers, polyisobutylene, ethylenevinyl acetate, and the like.

Very generally, it will be found that the polyethylene based copperadhesive composition of the invention will comprise 60 to 97, preferably80 to 95, and most preferably 85 to 92 weight percent of the low densitypolyethylene blended with a balance of elastomer such as butyl rubber,polyisobutylene, or ethylene propylene copolymer.

This blend is then grafted with from about 0.02 to 20, preferably 0.1 to10, and most preferably 0.2 to 8 weight percent of acrylic acid orglycidyl acrylate. The grafting is preferably carried out in accordancewith the procedures of Steinkamp and Grail, Ser. No. 240,494, which hasbeen incorporated herein in its entirety by reference.

When referring to polypropylene based copper thermoplastic adhesiveformulation, it is also important to note that direct grafting orincorporation of acrylic acid or glycidyl acrylate into thepolypropylene per se results in little or minimal copper adhesivevalues, unless molt temperatures of at least 500° F. are used.

It is only when an ethylene/propylene copolymer component eitherelastomeric or in the form of a reactor copolymer or a similarelastomeric component such as described above, e.g. butyl rubber,polyisobutylene and the like, is introduced in minor quantities into thepolypropylene based formulation, followed by grafting with eitheracrylic acid or glycidyl acrylate that outstanding copper adhesionresults can be obtained.

The other important criteria when operating with polypropylene basedformulations, is that the grafting monomer (5) of choice are theglycidyl acrylates, since in those situations exceptionally highadhesion values to copper can be obtained, especially when compared to astandard of the industry such as Surlyn.

Very generally, it is found that blends of 60 to 97, preferably 80 to95, and most preferably 85 to 92 weight percent of a polypropyleneblended with a balance of elastomer or reactor copolymer and thengrafted with from about 0.02 to 20, preferably 0.1 to 10, and mostpreferably 0.2 to 8 weight percent of acrylic acid or, most preferably,glycidyl acrylate, will adhere to copper or copper alloy substrates.Glycidyl acrylate grafts are particularly oustanding for achievingmaximum copper adhesion.

The components of the copper adhesion compositions can be blendedtogether and grafted, or they can be grafted separately and then blendedand formulated together. The person skilled in the art will choosewhichver is most convenient.

Additional details need not be given here since the Ser. No. 240,494application has complete descriptions.

Although this application and invention is expressly directed tospecific, narrowly-defined thermoplastic and adhesive compositions,which display outstanding adhesion for copper, it is to be noted that animportant feature of this invention is that the preferred copperadhesion formulation contains either a reactor copolymer of ethylene andpropylene or an elastomeric component in relatively minor proportions.

This apparently increases the mobility of the adhesive composition andpromotes additional adhesion. However, the phenomenon is more broadlyapplicable than for just formulations prepared for copper adhesion.

It is applicable to all the grafted formulations disclosed not only inthis applicaton, but in related copending applications, which arecopending with Ser. No. 240,494.

Moreover, it has also been noted and discovered and is an importantfacet of the technology involved with these grafted formulations, thatinclusion of a relatively minor, e.g. 2 to 30, preferably 5 to 20, mostpreferably 5 to 15 weight percent of an elastomeric component such asdescribed above, results in a formulation, particularly as respects apolypropylene based formulation in which drastic quenching, such aswater soaking to promote adhesion is rendered unnecessary.

In other words, very good and perhaps maximum adhesion values can beobtained with polypropylene and high density polyethylene basedformulations in which a small elastomeric component is included withoutthe necessity for a quench. Obviously this is a process feature ofsignificant economic value.

The adhesive thermoplastic formulations of the invention can also bemore precisely defined by additional criteria, i.e. their melt-flow rate(MFR) or their melt index (MI). Generally, as this number increases, theability of the adhesive formulation to wet the copper substrateincreases. Therefore, the MFR or MI of the particular formulation usedwill vary over a range of from aout 1 to 300, preferably 2 to 50, andmost preferably 2 to 35.

Although glycidyl acrylate and acrylic acid monomers are especiallypreferred and demonstrated grating monomers for this invention, otherclosely related monomers would be expected to be equivalents.

The term reactor copolymer as used herein is intended to refer toisotactic crystalline polypropylene which has been modified as made inthe reactor with ethylene sequences, either alternating or in blocks toimprove its impact performance at low temperatures. This is a commoncommercial expedient.

It should also be emphasized that the elastomeric component can be addedto the base polymer when in the form of an impact blend, sometimesincorrectly referred to as impact copolymer. This blend will usuallyhave varying proportions of polypropylene, polyethylene and an elastomersuch as ethylene propylene copolymers.

The invention will be further illustrated by the following examples:

EXAMPLE 1

In this example a series of formulations containing various quantitiesof polypropylene or polyethylene were blended together, either with orwithout any additional modifying elastomeric or reactor copolymercomponents.

Either films or pads were prepared from the formulation and they weremelted between two copper strips, allowed to cook, and a standard ASTMpeel value determination was made on these strips.

The results are summarized below in Table I.

                                      TABLE I                                     __________________________________________________________________________    Copper/Thermoplastic Peel Adhesion Values                                                               Wt. %                                               Sample     (MFR)                                                                             --C.sub.2 --                                                                       Wt. % (M)                                                                           Monomer.sup.3                                                                        (Copper) Peel Value                          Sample #                                                                            Form.sup.1                                                                         (MI)                                                                              Content.sup.2                                                                      or (R).sup.2a                                                                       A.A.                                                                              G.A.                                                                             Lbs/11/2" Width                              __________________________________________________________________________    Propylene "Based" Formulations                                                (1)   Pad  350 0     0    6   -- 1                                            (2)   Film 7   6    10 M  1   -- 1.5-3.0                                      (3)   Film 31  6    10 M  5   -- 1.3                                          (4)   Pad  95  6    10 M  6   -- 1                                            (5)   Pad  230 7    15.sup.6                                                                            6   -- 1                                            (6)   Film 8   15   25 M  1   -- 1                                            (7)   Film 15  15   25 M  3   --   1-1.5                                      (8)   Film 5   30   50 M  1   -- 1-2                                          (9)   Film 10  25   25 R  7   -- 2-3                                          (10)  Film 5   25   25 R  --  3  13-16                                        (11)  Pad  5   25   25 R  --  3  12-14                                        (12)  Pad  30  6    10 M  --  2  20-22                                        LDPE "Based" Products                                                         (13)  Film (10)                                                                              >97        --  2  2                                            (14)  Film (25)                                                                              >96        3   --   1-1.3                                      (15)  Film (11)                                                                              >94        5   --   2-2.5                                      (16)  Film (2) >85        3   --  8-10.sup.4                                  (17)  Film (2) >85        3   -- 2-3                                           (18).sup.7                                                                         Film (-8)                                                                              >95        -3  -- 2-3                                           (19).sup.8                                                                         Pad  --  >90        --  --  8-9.sup.5                                   __________________________________________________________________________     .sup.1 Samples were prepared from either 1.5-2.5 mil film or 6-8inch          compression molded pads.                                                      .sup.2 In these samples, the ethylene (C.sub.2 --) is present either in       the form of an impact blend (M) or reactor copolymer (R). The (N) and (R)     notations are reported under the sample # heading. Samples having C.sub.2     -- values greater than 85% were prepared from LDPE.                           .sup.2a M is a blend of 20 wt. % high molecular weight isotactic              polypropylene, 40 wt. % high density polyethylene, and 40 wt. %               ethylene/propylene copolymer elastomer.                                       .sup.3 A.A. = Acrylic Acid, G.A. = Glycidyl Acrylate                          .sup.4 Sample contains 10 wt. % butyl rubber.                                 .sup.5 Sample was provided by a 3rd party.                                    .sup.6 15 wt. % ethylene propylene copolymer elastomer.                       .sup.7 Ethylene (acrylic acid copolymer). (Union Carbide DQDA2300)            .sup.8 Ionomer. (DuPont Surlyn).                                         

As can be seen from the data in the above Table, excellent results areobtained with respect to only a few specially formulated compositions,since just directly grafting the polypropylene or polyethylene witheither acrylic acid glycidyl acrylate is not adequate to provideoutstanding adhesion properties to copper.

Under normal conditions except the glycidyl grafted polypropylene willadhere to copper if the melt temperature is at least 500° F.

It is also an important part of the invention that the copper adhesiveformulations will also adhere very well to many other common ferrous andnonferrous metals, as well as thermoplastics, thermosets and othersurfaces. Examples of specific laminates include

    ______________________________________                                                  Copper +                                                                        ferrous metals                                                                aluminum                                                                      lead                                                                          zinc                                                                          mylar                                                                         nylon                                                                         nitrile type polymers                                                         wood                                                                          glass                                                             ______________________________________                                    

In addition any of the metals listed can be bonded to each other withthe adhesives of this application as well as the Steinkamp-Grailapplication.

What is claimed is:
 1. A thermoplastic adhesive composition havingoutstanding adhesion to copper comprising a blend of(a) about 85 weightpercent of low density polyethylene; and (b) about 15 weight percent ofbutyl rubber, wherein said blend has been grafted with from 0.02 to 20weight percent of a monomer selected from acrylic acid.